Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)
The process is called phagocytosis – No Mark
1. Pathogen is engulfed by the phagocyte.
2. Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle;
3. Lysosomes fuse with vesicle releasing
digestive enzymes;
4. Lysosome enzymes break down the pathogen.
5. Waste materials are ejected from the cell by exocytosis;
Describe how a phagocyte destroys a pathogen present in the blood (3)
- Engulfs;
- Forming vesicle/phagosome and fuses with lysosome;
- Enzymes digest/hydrolyse;
Give two types of cell, other than pathogens, that can stimulate an immune response (3)
- (Cells from) other organisms/transplants;
- Abnormal/cancer/tumour (cells);
- (Cells) infected by virus;
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how (7)
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell secretes large amounts of antibody;
Explain how the humoral response leads to immunity (3)
- B cells specific to the antigen reproduce by mitosis.
- B cells produce plasma and memory cells
- Second infection produces antibodies in larger quantities AND quicker.
Describe and explain the role of antibodies in stimulating phagocytosis.
- Bind to antigen OR Are markers;
- Antibodies cause clumping/agglutination OR Attract phagocytes;
Describe the difference between active and passive immunity (6)
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells/memory cells;
- Passive involves antibody introduced into body from outside/named source;
- Active long term, because antibody produced in response to antigen;
- Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop/work, passive fast acting;
State why some antibodies are referred to as monoclonal
Antibodies produced from a single clone of B cells / plasma cells;
OR
Antibodies produced from the same B cell / plasma cell;
Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why (3)
- Specific) primary structure / order of amino acids;
- (Specific) tertiary / 3D structure / shape;
- (So) Only binds to / fits / complementary to one antigen;
Describe the structure of the human immunodeficiency virus (HIV) (5)
- RNA (as genetic material);
- Reverse transcriptase;
- (Protein) capsomeres/capsid;
- (Phospho)lipid (viral) envelope OR Envelope made of membrane;
- Attachment proteins;
Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections (4)
- High viral load leads to increased destruction of helper T/CD4 cells;
- Less activation of B cells/cytotoxic T cells/phagocytes;
- Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
- (less able to) destroy other microbes/pathogens OR (More able to) destroy mutated/cancer cells;
Describe the role of antibodies in producing a positive result in an ELISA test (4)
- (First) antibody binds/attaches /complementary (in shape) to antigen;
- (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
- (Substrate/solution added) and colour changes;
Antigen definition
Molecule that stimulates a immune response resulting in production of specific antibodies
Specific Immunity definition
Specific response to Specific antigen on surface of cell
Clonal selection (3)
Why is this method required?
- Specific TH cell binds to presented antigen via complementary receptor
- TH cell activated = clones produce many TH cells with complemntary recpector antigen
Not enough room in body to have lots of every T cell.
Increased num of cells = increased totaly energy demanded
Role of TH Helper cell (5)
- Specific TH cell binds to antigen presenting cell
- Releases cytokines = attracts phagocyte to infected area
- Releases cytokines = activates Tc cells
- Activates specific complementary B cells
- Forms memory TH cells
Role of Tc cells (4)
- Locates + destroys infected body cells that present correct antigen
- Binds to antigen presenting cell
- Releases protein = creates hole in cell surface membrace = destroys APC
Humoral response definition (3)
Where do B cells come from
Involves activation of B cells to produce antibodies
B cells must be stimulated by complementary TH cells by release of cytokines
Antibody definition
How is a specific antibody formed
Quaternary protein made in response to foreign antigen = specific binding site
From a specific plasma cell
How do antibodies assist in destruction of pathogens
Aggulation, Opsonisation, Lysis, Anti toxin
*Aggulation - Specific antibodies bind to antigen + clump them together
* Oponisation. - Marking phathogen so phagocyte can recognise + destroy them efficently
* Lysis - bind to antigen = causes destruction of pathogen membrane
* Anti toxin - Bind to toxin to prevent molecules from binding to target
* Preventing pathogen replication
Secondary response definition
Activation of memory cells from antibodies
HIV replication - using TH cells (7)
- Protein on HIV binds to protein found on TH cell
- Capsid fuses with cell surface membrane + releases viral mRNA and enzymes into TH cells
- HIV reverse trascripase converts viral mRNA to cDNA using host nucleotides
- cDNA moves into nucleus of T cells and is inserted into host genome = person infected
- T cells manufacture HIV particles
- Particles break away from TH cell forming lipid envelope with TH recpetor proteins
- Reduction in number of TH cells due to inactivation of TH cells
How antibiotics work (2)
- Antibiotics prevent bactieral making murein cell wall
- Bacteria unable to resist osmotic presure = burst open due to increased vol in cell
Explain why Antibiotics can’t be used for Viruses
- Viruses dont have any organelles to disrupt (use host cell organellese to carry out metabolic activites)
- Viruses have Capsid = doesnt allow antibiotic to damage virus
